Gulls 101 (1 Viewer)

Can anyone help me distinguish UK gulls from one another in a meaningful way? They are proving a real weak spot for me and no matter how many books & field guides I read I can't find a way of cementing it all in my head and getting it straight when I am out and about.

I'm currently confident dividing gulls into black-headed gulls & other gulls. That second category is quite large! I can do black-headed gulls all year round - I've mastered that one - but the black-backed, herring, common etc all have me stumped.

It's fine the books saying a great black-backed gull is bigger and darker than a lesser black-backed but these size comparisons don't really mean much to me when I see single birds. In time I will be able to judge relative sizes better by eye, without the reference bird also in sight, but not always at this stage in my birding.

So what diagnostic features should I be looking for with each species?

At the minute patch-listing somewhere like London WWT is tricky when I don't know all the different gulls. I know the main ones are all out there in the flocks so have ticked great black-backed, lesser black-backed, herring and so on but I couldn't confidently pick each of them out of a line-up of gulls. I feel like this is one of those things I need to learn.

I forgot about the Opus (how could I?) and have just been consulting that for some help on the main gull types I expect to encounter. From what I have read I reckon:

The massive gulls that make me think "Wow, I didn't realise gulls got that big, he's huge" are all going to be great black-backed. They may be immature and not have the full colouring but the size should be a giveaway.

Is wing colour and leg colour the best way to distinguish between lesser black-backed & herring gulls? Pinkish legs on a herring gull, which has paler grey wings than an LBB? What's the size difference like between the two species?

And what about LBB v yellow-legged gulls? They look very similar to me, based on the Opus photos - yellow legs, yellow bills with red spots and medium-dark grey backs. Is environment, size or some other factor the best way to separate them?

Another tip is to find out local populations / probabilities, for different times of the year - not sure what it would be in SW London, but up here (Northumbs), roughly:

Abundant:
Herring - thousands, all year
Lesser Black-back - hundreds in summer, odd ones in winter
Greater Black-back - odd ones in summer, hundreds in winter
Common - odd ones in summer, hundreds in winter
Kittiwake - thousands in summer, tens in winter
Black-headed - hundreds, all year

Uncommon:
Glaucous - odd ones in winter
Iceland - odd ones in winter
Mediterranean - odd ones in spring/summer, tens in autumn/winter
Little - odd ones, occasionally tens, in summer
Sabine's - odd ones in autumn after NW gales

Major rarities:
("don't expect to find these until you're very experienced, listen out for reports")
Yellow-legged
Caspian
Ring-billed
Ivory
Ross's
Bonaparte's
Laughing
Franklin's

See if you can construct a similar list for your area. It'll help you to know what you're likely to find.

Unfortunately there's no one easy way with the larger gulls as this is one of the most complex of bird ID's to master.

For a starting point I guess for adults the upper-parts colouration and tone could be classed into a sliding scale but there are variations.

Black - Great black-backed Gull and Lesser Black-backed Gull of the race / form intermedius (little to no contrast between upper parts and wing tips)

Very dark slaty grey - Lesser Black-backed Gull of the race graellsii, the common UK form, (slight contrast between upper-parts and black wing-tips)

Mid grey - Yellow-legged Gull, northern Herring Gull (argentatus), Caspian Gull (obvious contrast between uppaer-parts and black wing tips)

Paler Grey - Herring Grey (striking contrast between the upper-parts and black wing tips ie grey/black.

Any black-backed Gull with yellow-legs is a Lesser Black-backed Gull and any black-backed gull with pink legs is a Great Black-backed Gull. This statement excludes hybrids)

Grey backed gulls with pink legs are likely to be Herring Gull whilst those with yellow-legs are likely to be Yellow-legged Gull but note some populations of Herrings that sometimes occur in the UK can show yellow or at least yellow tinged legs but these are uncommon at best.

Caspian Gull generally has fleshy pink legs but can be flushed up to yellow in breeding season.

The above only really touches on full adults and some birds that are not fully adult, though may look it, may have slightly different leg colours. In addition light conditions for judging upper parts can be a factor with the best light be nuetral overcast days whilst bright sunny days can play havoc making yellow-legged gulls look extremely dark at some angle thus inviting confusion with with Lesser Black-backed Gull.

Then there's using structure as a key point as well as primary pattern however as you've said lone birds can be a problem so for determining whether a single dark backed gulls is large or mid sized, bulky or slender etc will come with experience.

As said there's no quick fix to large gulls and it will just come down to continued observation.

As for non adult plumages......well that's an even more of a challenge

A good book to use is "Gull of Europe Asia and North America" by Malling Olsen and Larson published by Helm. Although there are many gulls that you won't encouter in the UK, the descriptions and variations are very good. Also If you think you have a rarity, knowning the features of the other species will help in ruling them or or confirming the id. Many of the larger taxons are so similar and cross bred, it is more of a sliding scale based on geography rather than a clear cut species identifaction. Reading the help given and the explanations of the gull experts on this forum is enormously useful, even if that type of gull is not normally in your area. Often it is a case of elimination and looking closer at the possibilities that are left. The suggestions from Nutcracker, above, are also very good. I'm in the early stages of gull identifaction, welll bird id in general, so I take lots of photos in different light, weather etc. and compare them with other photos or books when I get home. There is no easy way to learn, but using tools to help that knowledge grow is extremely useful. A lot of older more experienced birders that started before the digital age, tend to look down on the use of modern methods to confirm ids, but they have the advantage of knowledge gleaned slowly over many, many years. Those of us playing catch up have a much steeper learning curve.

Thanks for the comprehensive responses, there is a lot for me to go through there and try and get my head round. I suspect I will be reading through this thread many times before I take it all in, and even then I suspect I will come back from sightings unsure of what I have really seen and will no doubt turn to the information in here as a guide.